1. Field of the Invention
The present invention relates to a rangefinder apparatus for measuring the distance to a target object; and, in particular, to an active type rangefinder apparatus used in a camera or the like.
2. Related Background Art
Conventionally known as an active type rangefinder apparatus used in a camera or the like is one having light-detecting means for detecting light reflected from target object and outputting near-side and far-side signals corresponding to the distance to the target object, comparing the far-side signal with a preset clamp signal in terms of magnitude, calculating an output ratio signal from the ratio between the greater signal determined by the comparison and the near-side signal, and converting the output ratio signal into a distance signal according to a converting expression varying depending on the value of output ratio signal as disclosed in Japanese Patent Application Laid-Open No. HEI 10-274524.
This rangefinder apparatus is aimed at obtaining rangefinding results on a par with those of a conventional system using both the light quantity and rangefinding in a short period of time without enhancing its circuit scale, so as to determine the distance to the target object uniquely and stably even when the distance is long.
Meanwhile, in this kind of rangefinder apparatus, output ratio signals may be computed repeatedly upon a plurality of light emitting operations, so that an integrating capacitor is charged according to these output ratio signals. In this case, an A/D conversion may be carried out in order for a CPU to process the charged voltage of integrating capacitor, so that the distance to the target object is calculated according to thus A/D-converted value.
However, there is a fear of conversion errors occurring upon an A/D conversion due to the roughness in dividing number for the A/D conversion. In a rangefinder apparatus carrying out rangefinding operations a plurality of times and taking their average as a rangefinding result, there is a fear of conversion errors upon A/D conversions being superimposed on each other so as to yield a large error.
In order to overcome such technical problems, it is an object of the present invention to provide a rangefinder apparatus which can reduce conversion errors upon A/D conversions, thereby improving its accuracy in rangefinding
For achieving such an object, the present invention provides a rangefinder apparatus comprising light-projecting means for projecting a light beam toward a target object; light-receiving means for receiving reflected light of the light beam projected to the target object and outputting an output signal corresponding to a distance to the target object; integrating means for charging or discharging an integrating capacitor according to the output signal of the light-receiving means; and converting means for A/D-converting a voltage of the integrating capacitor after an end of a rangefinding operation in which a predetermined number of light-projecting actions by the light-projecting means, light-receiving actions by the light-receiving means, and integrating actions by the integrating means are repeated; wherein a plurality of rangefinding operations are carried out with a different number of repetitions therein, and the distance is detected according to respective A/D-converted values obtained by A/D conversions after the rangefinding operations.
In the rangefinder apparatus in accordance with the present invention, the number of repetitions of light-projecting actions by the light-projecting means, light-receiving actions by the light-receiving means, and integrating actions by the integrating means in each rangefinding operation may be set so as to yield a different A/D-converted value.
In the rangefinder apparatus in accordance with the present invention, the number of repetitions of light-projecting actions by the light-projecting means, light-receiving actions by the light-receiving means, and integrating actions by the integrating means in each rangefinding operation may be set so as to yield a different conversion error value in the A/D-converted value.
Since the number of repetitions differs among individual rangefinding operations in the present invention, conversion errors occurring upon A/D conversions fluctuate, whereby conversion errors can be prevented from becoming greater. As a consequence, the rangefinding accuracy can be improved.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.